Voxel to Mesh Watertightness Question
Eric-Vin opened this issue · comments
I'm trying to convert a voxel grid exactly to a mesh, i.e. the resulting mesh should contain the exact volume of the original voxel grid. I'm having a problem with the resulting watertightness though, as it looks like some of the edges are connected to 4 faces, which conflicts with Trimesh's definition of watertightness (exactly 2 faces to every edge). Is it possible to do such a conversion from voxels to meshes exactly in Trimesh?
I've attached an image illustrating the problem, with fix_broken_faces having been used to color the problematic faces red.
Hey, yeah does it work if you disable vertex merging? Is the "voxel" input a mesh? You probably need to pass Trimesh(..., process=False) wherever the mesh is being created?
Thanks for the response! I suspect it would work but I'm using the triangles to_kwargs constructor so I think I'll have to refactor to use faces and vertices to try it. I'm working from a Trimesh VoxelGrid and creating triangles for each of the faces on the surface, so I get a mesh that represents the exact same space. My main concern is if I turn off processing upon creation and that mesh gets used in a boolean operation down the line, it might not be a volume on the way out if processing is applied internally. Is there a way to represent this sort of thing as a proper watertight mesh in Trimesh with the vertices merged/processing applied?
Here's my code for reference if you want to see what I'm doing. It's a rough prototype but the goal is to more rapidly construct what you would get from unioning all the boxes from the multibox VoxelGrid method together:
def mesh(self):
# Extract values for original voxel grid and the surface of the voxel grid.
dense_encoding = self.voxelGrid.encoding.dense
hpitch = self.voxelGrid.pitch[0] / 2
hollow_vr = trimesh.voxel.VoxelGrid(
trimesh.voxel.morphology.surface(self.voxelGrid.encoding),
transform=self.voxelGrid.transform,
)
surface_indices = numpy.argwhere(hollow_vr.encoding.dense == True)
surface_centers = hollow_vr.indices_to_points(hollow_vr.sparse_indices)
# Determine which faces should be added for each voxel in our extracted surface.
point_face_mask_list = []
def index_in_bounds(index):
return all((0, 0, 0) <= index) and all(index < dense_encoding.shape)
def actual_face(index):
return (
not index_in_bounds(target_index)
or not dense_encoding[tuple(target_index)]
)
for i in range(len(surface_indices)):
base_index = surface_indices[i]
base_center = surface_centers[i]
face_mask = [0] * 6
# Right
target_index = numpy.asarray(
[base_index[0] + 1, base_index[1], base_index[2]]
)
if actual_face(target_index):
face_mask[0] = True
# Left
target_index = numpy.asarray(
[base_index[0] - 1, base_index[1], base_index[2]]
)
if actual_face(target_index):
face_mask[1] = True
# Front
target_index = numpy.asarray(
[base_index[0], base_index[1] + 1, base_index[2]]
)
if actual_face(target_index):
face_mask[2] = True
# Back
target_index = numpy.asarray(
[base_index[0], base_index[1] - 1, base_index[2]]
)
if actual_face(target_index):
face_mask[3] = True
# Top
target_index = numpy.asarray(
[base_index[0], base_index[1], base_index[2] + 1]
)
if actual_face(target_index):
face_mask[4] = True
# Bottom
target_index = numpy.asarray(
[base_index[0], base_index[1], base_index[2] - 1]
)
if actual_face(target_index):
face_mask[5] = True
point_face_mask_list.append((base_center, face_mask))
# Construct triangles for mesh
triangles = []
for base_center, face_mask in point_face_mask_list:
# Right
if face_mask[0]:
triangles.append(
[
base_center + [hpitch, hpitch, -hpitch],
base_center + [hpitch, hpitch, hpitch],
base_center + [hpitch, -hpitch, hpitch],
]
)
triangles.append(
[
base_center + [hpitch, hpitch, -hpitch],
base_center + [hpitch, -hpitch, hpitch],
base_center + [hpitch, -hpitch, -hpitch],
]
)
# Left
if face_mask[1]:
triangles.append(
[
base_center + [-hpitch, hpitch, -hpitch],
base_center + [-hpitch, -hpitch, hpitch],
base_center + [-hpitch, hpitch, hpitch],
]
)
triangles.append(
[
base_center + [-hpitch, hpitch, -hpitch],
base_center + [-hpitch, -hpitch, -hpitch],
base_center + [-hpitch, -hpitch, hpitch],
]
)
# Front
if face_mask[2]:
triangles.append(
[
base_center + [hpitch, hpitch, -hpitch],
base_center + [-hpitch, hpitch, hpitch],
base_center + [hpitch, hpitch, hpitch],
]
)
triangles.append(
[
base_center + [hpitch, hpitch, -hpitch],
base_center + [-hpitch, hpitch, -hpitch],
base_center + [-hpitch, hpitch, hpitch],
]
)
# Back
if face_mask[3]:
triangles.append(
[
base_center + [hpitch, -hpitch, -hpitch],
base_center + [hpitch, -hpitch, hpitch],
base_center + [-hpitch, -hpitch, hpitch],
]
)
triangles.append(
[
base_center + [hpitch, -hpitch, -hpitch],
base_center + [-hpitch, -hpitch, hpitch],
base_center + [-hpitch, -hpitch, -hpitch],
]
)
# Top
if face_mask[4]:
triangles.append(
[
base_center + [hpitch, -hpitch, hpitch],
base_center + [hpitch, hpitch, hpitch],
base_center + [-hpitch, hpitch, hpitch],
]
)
triangles.append(
[
base_center + [hpitch, -hpitch, hpitch],
base_center + [-hpitch, hpitch, hpitch],
base_center + [-hpitch, -hpitch, hpitch],
]
)
# Bottom
if face_mask[5]:
triangles.append(
[
base_center + [hpitch, -hpitch, -hpitch],
base_center + [-hpitch, hpitch, -hpitch],
base_center + [hpitch, hpitch, -hpitch],
]
)
triangles.append(
[
base_center + [hpitch, -hpitch, -hpitch],
base_center + [-hpitch, -hpitch, -hpitch],
base_center + [-hpitch, hpitch, -hpitch],
]
)
out_mesh = trimesh.Trimesh(**trimesh.triangles.to_kwargs(triangles))
assert out_mesh.is_volume
return out_mesh